Electrophysiological characteristics of lead position-dependent electrogram uninterrupted transition during left bundle branch pacing.

Background: The interrupted technique of left bundle branch pacing (LBBP) limits the continuous monitoring of paced electrocardiogram and intracardiac electrogram (EGM) transitions, which may result in overlooked or misinterpreted subtle transitions.

Objectives: This study aimed to explore the electrophysiological characteristics of lead position-dependent EGM continuous transitions to evaluate lead depth and to investigate the clinical significance of transseptal pacing modalities.

Methods: A continuous pacing and recording technique enabled by a rotatable connector was used to allow the real-time monitoring of progressive changes in paced EGM and electrocardiographic morphology. Careful observations were conducted to evaluate whether there were significant changes in the amplitude and morphology of the ventricular current of injury (COI), R-wave peak times in leads V₁ and V₆, QRS duration, and impedance at different interventricular septal depths.

Results: The study included 105 patients. Nonselective LBBP was achieved in 94 patients (89.5%), of whom 88 (83.8%) achieved selective LBBP (SLBBP). Left ventricular septal pacing was confirmed in 11 patients (11.5%). The amplitude of ventricular EGM predictably changed with radial septum depth and peaked in the interventricular septum (26.3±11.3 mV). As the lead was inserted into the left ventricular subendocardium, the ventricular COI declined to a level approximating that of the right septum (11.7 ± 6.3 mV for SLBBP vs 10.4 ± 5.8 mV for right ventricular septal pacing). When selective left bundle branch capture occurred, significant morphological transitions in the ventricular COI were observed in the unfiltered EGM.

Conclusion: The continuous recording technique provides a more detailed understanding of pacing lead radial depth throughout implantation. COI amplitude and morphology variations can identify different pacing modalities, particularly in recognizing SLBBP.